I've not ever posted here before that I can recall now, though I've been a long time member... Creative Cow has always been an excellent resource for ideas, tips and troubleshooting for me so thanks to all for many years of this valued resource!

I have consistently used this machine for the last year with next to no issue until v13 of Premiere Pro, whereupon Premiere or Media Encoder consistently hangs, crashes to desktop, or reboots upon an Export operation when running with Metal or Open CL acceleration. It also tends to hang or crash at other times as well, such as during attempts to send a project from Premiere to Media Encoder when hitting 'Queue', or when using Shift+Option launch on Premiere to flush caches and prefs.

I do not encounter any issues when working in Premiere Pro during the editing process with Metal acceleration on. I edit mostly H264 4K movs from a GH4 or 4K MXFs from an FS7. I render H264 MP4 files or ProRes Mov files usually at 1080p. Playback during editing is not smooth for much of the time, and I need to let it catch up sometimes but I expect that with these kinds of files, and for what I'm doing it is smooth enough. What's important to me is that it behaves, and the machine did all the editing things I could throw at it without falling over including exporting, right up until recently. Now it does all the editing things I can throw at it without falling over right up until I hit that Export button.

I have tried to troubleshoot as far as I am able with this:
Tried previous versions of the software through Adobe Cloud options,
Checked and revised various folder permissions based on other crash related reported issues scoured from the internet,
Various Premiere project level tricks such as flushing and rebuilding media caches, trashing and rebuilding preferences,
A system reimage by my institutions IT bods and subsequent reinstall of Adobe CC applications,
OSX built in ram test initiated when holding D on boot,
A boot level ram test using memtest that came back with no errors

The crash on Export is consistent and the same no matter what I try. The file object is created at zero kb size, the progress bar window appears but there's no activity, and a minute or two later the machine freezes and reboots on its own.

Nothing in what I can find and read with related changes to hardware acceleration in the latest versions suggests that I shouldn't be able to use acceleration for this sort of work. Using software mode may be a recourse but doesn't really seem like a 'fix' for something that wasn't broken before, and faster performance is important. I'm wondering if this sounds like a hardware issue with the machine, or whether other people have encountered anything similar changing to v13. It's just so strange to me since it worked so consistently well up until then.

[Andrew Thomson]"I edit mostly H264 4K movs from a GH4 or 4K MXFs from an FS7. I render H264 MP4 files or ProRes Mov files usually at 1080p."

You have an older Mac with a small amount of VRAM. If you're attempting to export 4k sequences with H264 4k media you're putting a lot of CPU strain on your system. Have you looked at your CPU usage (in Activity monitor) during the export process?

I would transcode all of your H264 media to an edit-friendly codec (cineform, Prores or DNxHD) and then attempt the export. My guess is your problem will go away.

I do not believe that it is as simple as the computer is too slow for this work. I've had this workflow for a year with this machine. It isn't that before v13 I had less crashes - before v13 I didn't have any crashes at all. I know editing with H264 files in 4k is not smooth or fast. With acceleration on the workflow is smooth enough. The Mac pro doesn't exhibit issues or crashes during editing. It also happily renders in software mode so its not falling over because of the material itself.

I am currently using an Apple laptop that is older still borrowed from another team in my group as a stand in, and I do the very same work with it. The only difference is the editing process is slower still and I can't do much with it while its rendering... but it renders.

You did make me think about something I haven't tried though regaridng proxies and using differently encoded files.

I couldn't get Premiere to make any proxies because it crashes when sending to Media Encoder as I described previously. I did however use another application (on the Mac Pro) to encode a set of ProRes encoded files at 4k from the original 4k files and they too perfrom fine during editing but crashes persist upon export.

I assume you already dumped cache en reset preferences and the usual suspects. So it seems something hardware related then.

Apple's Trashcan has a poor reputation concerning its GPU's. But since you are editing GPU-accelerated and just not exporting, it is a bit of a mystery. And since you've had success in the past, it is not super likely your D500's are broke either. But judging from your video it is clearly the GPU giving you the issues though. Have you tried a GPU-accelerated export in other software than Adobe's? Just to make sure it is not occuring with other developers as well. Maybe try DaVinci Resolve 15 and check the GPU when exporting.

I would bet on an unfortunate mismatch between the 13.1.4 version of Premiere and the GPU drivers in 10.14.6 MacOS. I have a D500 nMPro on High Sierra 10.13.6 as an encoding machine and I don't recall any issues with it on our shop using metal or openCL. But I should confirm that with our assistant.

Sadly since you can not control drivers in MacOS, so you may only be able to A/ wait for Adobe to fix the mismatch (if it is confirmed as a mismatch) or B/ try a downgrade of the OS to High Sierra (this will mean a full clean install).

I also just remembered: this version of PPRO (v13.1) is also one with 'added support' for multi-GPU workflows. That could also be a lead: this version in particular is maybe 'coded differently' than the ones before it. This was some info on multi-gpu and egpu in the 13.1 version:

One thing I feel completely inept about is not realising there has been a GPU monitor in the Activity Monitor this whole time until seeing the video you posted... kill me now.

I went back into the Mac Pro to try some things with the GPU monitor enabled, and the crashes occur even more quickly and frequently... during playback and before attempting to render. It's as if just running the monitor stresses it out.

This has been useful to close in on the GPU as the probable cause, and gives me something more solid for the IT bods in my institution to investigate as well.